annular combustion chamber for a turbomachine

ABSTRACT

An annular combustion chamber for a turbomachine, such as a jet engine or a turboprop engine for an aircraft, including at the downstream end of one of its external or internal walls of revolution an annular flange for fastening to a casing of the turbomachine, the downstream end of the other wall of revolution of the chamber including a bearing mechanism which are spaced apart from another casing of the turbomachine when cold and bear radially on this casing when hot.

The invention relates to an annular combustion chamber for a turbomachine, and also to a turbomachine that is fitted with said combustion chamber, in particular a turbomachine such as an airplane turboprop or turbojet.

An annular combustion chamber of a turbomachine comprises annular walls constituting bodies of revolution, respectively an inner wall and an outer wall, the walls being formed at one end with annular flanges enabling the chamber to be fastened by means of bolts respectively to inner and outer casings of the turbomachine.

The annular flanges need to be sufficiently stiff to ensure that the resonant frequencies of the combustion chamber are higher than the frequencies of vibration of the turbomachine in operation. Such stiffness for the flanges requires them to have dimensions, and therefore weight, that if reduced excessively can lead to vibratory phenomena in the combustion chamber with a risk of severe mechanical incidents.

The stiffness of the flanges also gives rise to high levels of stress in the flanges while the turbomachine is in operation: the combustion chamber is then subjected to high temperatures and it is fastened by means of the flanges to casings at a temperature that is well below that of the combustion chamber, such that stresses that are due to differences of thermal expansion between the chamber and the casings are concentrated in the flanges, to the detriment of their lifetime.

A particular object of the present invention is to limit the stresses in the fastener flanges while avoiding problems associated with combustion chambers withstanding vibration.

In corresponding manner, another object of the invention is to reduce the weight of the fastener flanges.

To this end, the invention provides an annular combustion chamber for a turbomachine, the combustion chamber comprising two annular walls forming bodies of revolution, respectively an inner wall and an outer wall, one of the walls including an annular flange for fastening the chamber to a casing of the turbomachine, the chamber being characterized in that the other annular wall has bearing means designed, when cold, to be spaced apart from another casing of the turbomachine, and, when hot, to bear radially against said other casing.

The combustion chamber of the invention is thus fastened via a single inner or outer annular flange to one of the casings of the turbomachine, and when hot its greater thermal expansion causes it to bear additionally against another casing of the turbomachine. The stresses that are generated by the thermal expansion difference between the chamber and the casing appear in the flanges only from the moment when the additional bearing against the other casing starts. Overall, the stresses in the annular fastener flanges of the combustion chamber are less than those that are observed in the prior art.

According to another characteristic of the invention, the bearing means are connected to the wall of the chamber via at least one elastically-deformable zone.

Thus, when the additional bearing is established against the other casing of the turbomachine, the flexibility of this zone serves to limit the increase of stress in the annular fastener flange against the first casing.

In a preferred embodiment of the invention, the bearing means comprise a cylindrical end wall connected to the annular wall of the chamber via a wall inclined relative to the axis of said chamber.

The inclined wall may include orifices for passing ventilation air.

In a first embodiment, the annular fastener flange is carried by the outer annular wall of the chamber and the bearing means are carried by the inner annular wall of said chamber.

In a variant, the annular fastener flange is carried by the inner annular wall of the combustion chamber and the bearing means are carried by the outer annular wall thereof.

The invention also provides a turbomachine such as an airplane turboprop or turbojet, the turbomachine being characterized in that it includes a combustion chamber of the type described above.

Advantageously, the turbomachine has a casing that includes a cylindrical portion against which the bearing means of the combustion chamber are designed to bear when hot.

Preferably, when hot, the bearing means of the chamber are in sliding contact with said cylindrical portion of the casing. This arrangement enables the combustion chamber to expand in operation so as to come into contact against a casing of the turbomachine.

Typically, when cold, the clearance between the bearing means of the combustion chamber and the casing of the turbomachine is of the order of one-tenth of a millimeter.

The invention can be better understood and other characteristics, details, and advantages thereof appear more clearly on reading the following description made by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic half-view in axial section of an annular combustion chamber of the prior art; and

FIGS. 2 and 3 are two views similar to FIG. 1 showing two embodiments of the invention.

In FIG. 1, reference 10 designates an outer casing of a turbomachine such as an airplane turbojet, reference 12 designating an annular combustion chamber housed inside the casing 10 downstream from a compressor (not shown) that feeds the combustion chamber 12 with air under pressure via a diffuser 14.

The chamber 12 diverges and comprises a radially outer annular wall 16 forming a body of revolution and a radially inner annular wall 18 forming a body of revolution, which walls are connected together at their upstream ends by a chamber end wall 20 and by a fairing 22 that includes orifices for passing fuel injectors 24 carried by the casing 10 and drawn in dashed lines.

The downstream ends of the annular walls 16, 18 of the chamber 12 have respective annular flanges 26, 28 enabling the chamber 12 to be fastened to a corresponding annular flange 30 of the outer casing 10 and to an annular flange 32 of an inner casing 34 that extends from the diffuser 14 along the inner wall 18 of the combustion chamber.

In the example shown, the annular flanges 26, 28 are connected to the downstream ends of the annular walls 16, 18 by respective annular link walls 36, 38.

The annular flanges 26, 28 and their walls 36, 38 linking them to the walls 16, 18 of the chamber 12 need to present sufficient stiffness to ensure that the resonant frequencies of the combustion chamber are higher than the frequencies of vibration of the turbomachine in operation. However, the greater the rigidity of these flanges and the walls 36, 38, the greater the levels of stress that develop therein during operation as a result of the thermal expansion difference between the chamber 12 and the casings 10 and 34, thereby reducing the lifetime of said flanges and link walls.

The invention enables this problem to be solved in a manner that is simple, inexpensive, and satisfactory, as described below with reference to FIGS. 2 and 3.

FIG. 2 is a diagrammatic half-view in axial section showing an annular combustion chamber 42 of the invention, which combustion chamber converges in this example and is fed with air under pressure, not by an axial diffuser 14 as for the combustion chamber 12 of FIG. 1, but by a radial diffuser 44 associated with an annular flow-straightener 46, the diffuser 44 being mounted at the outlet from a centrifugal compression stage (not shown).

It can be observed that the present invention is naturally applicable to annular combustion chambers of the type shown in FIG. 1.

The annular chamber 42 of FIG. 2 has two annular walls forming bodies of revolution, respectively an outer wall 48 and an inner wall 50, which walls are generally frustoconical in shape with their upstream ends connected together by an annular chamber end wall 52 having conventional means for receiving the heads 54 of fuel injectors that are carried by an outer casing 40 of the turbomachine.

The downstream end of the inner annular wall 50 is connected by a frustoconical annular wall 56 to an annular flange 58 that is fastened by bolting to a corresponding annular flange 60 of an inner casing 62 carrying the diffuser and flow-straightener 44, 46.

The downstream end of the outer annular wall 48 is connected via a frustoconical wall 64 to an end cylindrical wall 66 that extends along a cylindrical downstream portion 68 of the outer casing 40.

The cylindrical end wall 66 and the cylindrical portion 68 of the outer casing in this example are substantially parallel to the longitudinal axis 70 of the turbomachine, which constitutes the axis of rotation of the compressors and of the turbines of this turbomachine.

The cylindrical end wall 66 of the combustion chamber 42 is parallel to the cylindrical portion 68 of the outer casing 40 and, when cold, it is separated therefrom by clearance that is small, as shown in FIG. 2. This clearance is designed to remain when the turbomachine is started and while it is idling.

As its speed of rotation increases, e.g. for takeoff of an airplane fitted with a turbomachine, the radial thermal expansion of the combustion chamber 42 is considerably greater than that of the outer casing 40, such that the radial clearance between the end wall 66 of the combustion chamber and the cylindrical portion 68 of the outer casing 40 disappears, with the end wall 66 of the chamber bearing radially against the cylindrical portion 68 of the casing 40. This bearing force provides additional fastening for the combustion chamber to the turbomachine and makes this fastening stiffer, such that the resonant frequency of the combustion chamber increases, thereby remaining greater than the frequencies of vibration of the turbomachine in operation.

The flexibility of the frustoconical walls 56 and 64 and the clearance when cold between the bearing portion 66 and the cylindrical portion 68 are designed to reduce, as much as possible, any development of stresses in the connection zones between the flange 58 and the wall 50 and between the bearing portion 66 and the wall 48, while nevertheless ensuring that the cylindrical wall 66 bears firmly against the cylindrical portion 68 of the outer casing 40 when hot.

The sliding contact between the cylindrical wall 66 and the portion 68 of the casing 40 encourages this overall reduction in stresses.

As shown, the frustoconical wall 64 may include orifices 65 for passing ventilation air, thereby contributing to making it more flexible.

The order of magnitude of the radial clearance when cold between the cylindrical wall 66 and the cylindrical portion 68 of the casing is one-tenth of a millimeter.

FIG. 3 shows a variant embodiment of the invention in which the combustion chamber 42 is fastened to the outer casing 40 by an annular flange 72 connected to the downstream end of its outer annular wall 48 by a frustoconical portion 64.

Its inner annular wall 50 is connected by a link wall 74 to a cylindrical end wall 76 of axis that coincides with the longitudinal axis 70 of the turbomachine.

In the example shown, this cylindrical end wall 76 extends upstream and is engaged in a cylindrical annular groove formed by a rim 78 on a wall 80 that is secured to the inner casing 62 of the turbomachine. Depending on the space available, the cylindrical wall 76 may extend downstream. The wall 80 has a cylindrical portion 82 parallel to the cylindrical end wall 76 of the combustion chamber and spaced apart therefrom when cold by radial clearance having an order of magnitude of one-tenth of a millimeter. When hot, this radial clearance disappears and the cylindrical end wall 76 of the combustion chamber bears radially against the rim 78 of the inner casing.

The annular flange 72 is connected to the outer annular wall 48 of the chamber via a frustoconical wall 64 similar to that described with reference to FIG. 2, and of stiffness that is determined to ensure that the combustion chamber 42 is properly supported and positioned when cold and while the turbomachine is idling. The flexibility of the wall 74 connecting the end wall 76 to the inner annular wall 50 of the chamber is determined so that when hot the thrust against the rim 78 of the inner casing, combined with the stiffness of the link wall 64, confers a resonant frequency to the combustion chamber 42 that is greater than the frequencies of vibration of the turbomachine in operation.

Otherwise, the essential means of the FIG. 3 variant embodiment remains the same as those described and shown in FIG. 2. 

1-11. (canceled)
 12. An annular combustion chamber for a turbomachine, the combustion chamber comprising: two annular walls forming bodies of revolution, respectively an inner wall and an outer wall, one of the walls including an annular flange for fastening the chamber to a casing of the turbomachine, wherein the other annular wall include bearing means configured, when cold, to be spaced apart from another casing of the turbomachine, and, when hot, to bear radially against the casing.
 13. An annular combustion chamber according to claim 12, wherein the bearing means is connected to the wall of the chamber via at least one elastically-deformable zone.
 14. An annular combustion chamber according to claim 12, wherein the bearing means comprises a cylindrical end wall connected to the annular wall of the chamber via a wall that is inclined relative to the axis of the chamber.
 15. An annular combustion chamber according to claim 14, wherein the wall inclined relative to the axis of the chamber includes orifices for passing ventilation air.
 16. An annular combustion chamber according to claim 14, wherein the wall inclined relative to the axis of the chamber is flexible.
 17. An annular combustion chamber according to claim 12, wherein the annular fastener flange carries the outer annular wall, the inner annular wall, and the bearing means via an end wall of the chamber.
 18. An annular combustion chamber according to claim 12, wherein the annular fastener flange carries the inner annular wall together with the outer annular wall and the bearing means via a chamber end wall.
 19. A turbomachine, such as an airplane turboprop or turbojet, comprising an annular combustion chamber according to claim
 12. 20. A turbomachine according to claim 19, further comprising a casing including a cylindrical portion against which the bearing means of the combustion chamber are configured to bear when hot.
 21. A turbomachine according to claim 19, wherein, when hot, the bearing means of the combustion chamber makes sliding contact with the cylindrical portion of the casing.
 22. A turbomachine according to claim 19, wherein a clearance, when cold, between the bearing means of the combustion chamber and the cylindrical bearing portions of the casing is of an order of one-tenth of a millimeter. 